Modeled changes to the Great Plains low‐level jet under a realistic irrigation application

Abstract

Low‐level jets (LLJs) are relatively fast‐moving streams of air that form in the lower troposphere and are a common phenomenon across the Great Plains (GP) of the United States. LLJs play an important role in moisture transport and the development of nocturnal convection in the spring and summer. Alterations to surface moisture and energy fluxes can influence the planetary boundary layer (PBL) development and thus LLJs. One important anthropogenic process that has been shown to affect the surface energy budget is irrigation. In this study, we investigate the effects of irrigation on LLJ development across the GP by incorporating a dynamic and realistic irrigation scheme into the Weather Research and Forecasting (WRF) model. WRF simulations were conducted with and without the irrigation scheme for the exceptionally dry summer of 2012 over the GP. The results show irrigation‐introduced changes to LLJ features both over and downstream of the most heavily irrigated regions in the GP. There were statistically significant increases to LLJ speeds in the simulation with the irrigation parameterization. Decreases to the mean jet core height on the order of 50 m during the overnight hours were also simulated when irrigation was on. The overall frequency of jet occurrences increased over the irrigated regions by 5–10%; however, these differences were not statistically significant. These changes were weaker than those reported in earlier studies based on simple representations of irrigation that unrealistically saturate the soil columns over large areas over a long period of time, which highlights the importance and necessity to represent human activity more accurately in modeling studies.

Sensitivity of Low-Level Jets to Land-Use and Land-Cover Change over the Continental U.S.

“…Following [3] and [14], a LLJ in this study is identified if the simulated vertical wind profile at a particular grid point meets the following two criteria: (1) A wind speed maximum no less than 12 m s −1 must be present below 3000 m above ground level (AGL) and (2) the decrease of wind speed from the maximum to the next minimum above (or 5000 m AGL, whichever is lower) and below (or surface, whichever is higher) must be no less than 6 m s −1 . These criteria are applied at every surface grid point in the domain and at all the 3-hourly model output times.…”

“…Parish and Oolman [13] used the Weather Research and Forecasting Nonhydrostatic Mesoscale Model (WRF-NMM) to examine the importance of topography on LLJ formation and found that heating over sloping terrain leads to stronger background geostrophic flow that contributes to maximum simulated LLJs over the Great Plains through the inertial oscillation mechanism following the decoupling of the frictional layer from the free atmosphere above. Recently, Arcand et al [14] employed the WRF model to investigate how irrigation, a common practice in the southern Great Plains, may affect LLJ properties and identified changes in LLJ characteristics over and especially downstream of heavily irrigated regions.…”

“…In this study, the potential impact of projected land-use and land-cover (LULC) change on LLJ climatology in the continental U.S. (CONUS) is investigated using regional climate simulations. It has been shown previously that LLJs are sensitive to surface parameters, such as soil moisture, roughness length, albedo, and heat storage, that depend heavily on LULC patterns [12,14,20]. With the ongoing population and economic growth in the U.S., LULC is projected to change and the question is whether and how much the projected changes in LULC will modify or alter LLJ behavior in the U.S., especially over the central U.S. where jets are prevalent and significant changes in LULC are projected.…”

Influence of Irrigation on Diurnal Mesoscale Circulations: Results From GRAINEX

“…Despite considerable work by previous studies, there remain gaps in understanding the interactions between irrigation and mesoscale circulations such as the slope wind. Most studies that address the effects of irrigation (and soil moisture) on mesoscale circulations are theoretical in nature or utilize relatively coarse analysis grids that often poorly represent mesoscale phenomena (e.g., Anthes, 1984; Arcand et al., 2019; Campbell et al., 2019; Huber et al., 2014; Kueppers & Snyder, 2012; Ookouchi et al., 1984; Yang et al., 2020). This paper proposes to fill this gap using the extensive rawinsonde observations collected during the 2018 Great Plains Experiment (GRAINEX; Rappin et al., 2021) in Nebraska to characterize the impacts of irrigation on the Great Plains diurnal slope wind.…”

Changes in Great Plains Low‐Level Jet Structure and Associated Precipitation Over the 20th Century

“…Improving mechanistic understanding, modeling, and forecasting of the GPLLJ has been a research priority for over half a century (e.g., Blackadar, 1957; Bonner, 1968; Du & Rotunno, 2014; Holton, 1967; Parish, 2017; Shapiro et al., 2016; Smith et al., 2019), spurred by the GPLLJ’s relevance to regional wind and water resources (e.g., Barandiaran et al., 2013; Wilczak et al., 2015), severe weather (e.g., Weaver et al., 2012), heatwaves (e.g., Thomas et al., 2020), aviation (e.g., Gultepe et al., 2019), and pollutant transport (e.g., Corsmeier et al., 1997). More recently, efforts to simulate future GPLLJ strength, northward extent, and seasonality (e.g., Tang et al., 2017; Wimhurst & Greene, 2020), including the effects of an ever‐increasing U.S. irrigation‐equipped area on the GPLLJ (e.g., Arcand et al., 2019; Yang et al., 2020), are trending.…”